1. Field of the Invention
The present invention relates to the generation of electrical power by wind and water electrical generating systems where a rotor shaft, being rotated by turbine blades, powers a hydraulic pump generating hydraulic pressure which is used to turn a hydraulic generator motor which spins a generator for generating electricity for distribution by an electric grid.
2. Description of the Prior Art
There has recently been a surge of interest in alternate energy sources for generating electricity by both the public and by the utility companies. The public's concern is pollution and the eventual depletion of carbon-based fuels; the utilities are concerned with the state and federal mandates requiring a higher percentage of their electricity output be produced from alternate energy sources. Solar, wind, and biomass are the main alternate energy sources now being purchased by the utilities. Residential solar has been around for years, commercial solar farms are presently being developed. There has been a lot of construction in the wind industry during recent years. The US has more wind generating systems than any other country.
Present day commercial wind turbines tend to be very large, often 40-50 stories tall. The rotor blades are long and slender. A nacelle is mounted atop a support tower. Inside the nacelle there is most often a synchronous generator coupled to the rotors through a planetary gearbox which increases the rotational speed for spinning the generator. Also in the nacelle there are numerous electronics for controlling the system, and conditioning the electrical power for the grid. Often there are dehumidifiers for conditioning the environment for the electronics.
Systems with step-up gear drive trains between the rotor and generator use high speed generators which use electromagnetic copper coils fed electricity from the generator. There has recently been interest and development work with direct-drive wind turbines. These systems do not use a geared transmission, therefore, they are called direct-drive systems. These systems use permanent magnets in the generator rotor. Since the direct-drive systems have no gear box, they have fewer parts and are lighter, and claimed to be more reliable. A very small percentage of the commercial wind generators today use direct-drive transmissions, development continues.
Water turbine development lags wind turbine development by several years. Water systems, which use water currents as the kinetic energy source rather than wind, are in the prototype development stage. There is, however, a lot of cross-over in the technologies of the two systems as they use similar step-up gear drive trains directly coupling the rotors to the generator. It is therefore anticipated that water systems development will catch-up rather quickly as more effort is devoted to water systems.
Conventional hydroelectric power generating systems use dams or barrages to divert water causing currents. Hydrokinetic systems, on the other hand, use free flowing water as the energy source. Reference is now made to U.S. Pat. No. 7,736,127, and US patent applications US2010-0187825 and US2010-0187826, all having the same inventor as the present application. These documents are incorporated as references to overview hydrokinetic technology and as disclosure documents in the present application.
Proposed or prototype developed hydrokinetic water systems to-date use either a geared transmission drive or a modification of the direct drive arrangement. That is, the rotors and generator are directly connected to each other, therefore, in close proximity to each other. They are enclosed in the nacelle of the generating system.
In the present application the turbine generates a hydraulic pressure, and the hydraulic pressure is used to spin a generator. The rotor blades and generator are not directly coupled by a mechanical drive-train, therefore, they may be distantly located as on the ground with wind systems or on the shore bank with water systems. The rotational mechanical energy from the rotors is transferred by a rotor shaft to a hydraulic pump which generates pressurized fluid. The hydraulic pressure is transferred through a pipe system to a hydraulic generator motor which spins a generator generating electricity.
The hydraulic drive approach of the present application would eliminate the need for a gearbox, therefore, generating systems would have less parts and the nacelle be lighter in weight. Problems with lubricating gear boxes have been known for years, and the problem is being experienced in commercial units today. There are also other advantages. If the generator were located on the ground, systems would be easier to install and maintain. As noted previously, commercial wind systems can be up to fifty stories tall requiring a crane for installation and sometimes for repair.
When the generator is located in the nacelle, numerous electronics are required to control the system and condition the power for use in the grid, that is, at approximately sixty cycles per second. Dehumidifiers are often needed in wind systems to condition the environment in the nacelle to protect the electronics. It is anticipated that the moisture situation in submerged water systems will be even more difficult to manage. It follows that fewer electronics in the nacelle would be desirable.
Both wind and water currents have turbulence which can cause vibrations in the rotors. These vibrations are often transferred through the gear box to the generator resulting in damage. Since the hydraulic approach decouples the rotor from the generator as there is no gearbox, this would be a solution to the vibration problem. The hydraulic drive-train could also increase the capacity factor, the time period a generator is actually producing electricity, for both wind and water systems. There is less inertia in starting the operating cycle of a hydraulic system compared to a mechanical gear drive from rest. The generating cycle would therefore start earlier, and the operating cycle last longer, thereby increasing the capacity factor.
Hydraulic pumps and motors have been widely used to drive systems in other industries for decades. The motors can be hydrostatic or hydrodynamic. The hydraulic pumps generally create a hydraulic pressure by pulling fluid from an open-system reservoir and create pressure by meshing gear teeth, rotating vanes, or by the action of gears or pistons. There are several types of pump designs as later discussed, commercially available from several companies including Volvo Hydraulics.
The pressurized fluid, usually synthetic oil, is directed to a hydraulic motor through a to-motor pipe and returned through a from-motor pipe. Hydraulic piping is widely used in hydraulic systems and commercially available. The technology for submerged piping has been recently advanced by the petroleum drilling industry which uses hydraulics for drilling and pumping. These hydraulic systems are often located miles below the ocean surface.
Hydraulic motors are combined with hydraulic pumps to form hydraulic drive systems. Hydraulic motors convert hydraulic pressure into torque or rotation, which is the rotational counterpart of a hydraulic cylinder. There are many designs for hydraulic motors, the most common designs being the gear, vane, axial plunger, and radial piston motors.
Multi pump assemblies can be used where multi pumps feed one hydraulic motor. In the present application for the water generator, one or more hydraulic pumps are coupled to a hydraulic motor which is further coupled to a generator causing it to spin generating electricity. The preferred embodiments in the present application are piston-type hydraulic pumps coupled to a bent axis hydraulic generator motors. It is noted that several types of hydraulic pump and motor combinations are possible for the presently disclosed application, thus, the preferred embodiment is not intended to be limiting.
Prior art systems generate electricity directly through either a mechanical gear drive train or a direct-drive connection, whereby there is a direct link between the rotors and the generator. The present invention generates hydraulic pressure which is used to spin the generator which may be distantly located. As discussed, there are several advantages to decoupling the rotors from the generator.
Hydraulics presently are used for other applications in the generating industry, for example, they can be used to form hydraulic transmission drives between the rotors and generator. Also, hydraulics can be used to control rotor pitch. A prior art publication relating to the use of hydraulic technology in the transmission of wind turbines is U.S. Pat. No. 7,418,820. These hydraulic transmission systems generally use a ring of cylinders arranged radial around the rotor shaft. As the shaft rotates it drives pistons into cylinders pressuring fluid which is used to power hydraulic motors, which in turn drives a generator. The 820 disclosure discloses a hydrostatic transmission which directly couples the rotors to a hydraulic pump. The transmission receives the hydraulic output and drives a generator. The transmission and generator are both located in the nacelle having a direct link to each other.
A major objective of the present invention is to decouple the rotors from the generator in a manner that the two can be located at a distance from each other. In addition, decoupling the two would help address the vibration problems in wind and water systems as well as ease installation and maintenance.
Hydraulics have been used in other industries to control rotor pitch for years, for example, in the helicopter industry. Reference is made to the aforementioned US2010-0187825 document as an example of the use of hydraulics in adjusting rotor pitch. The 0187825 document and other referenced documents cite several references in the power generating industry.
The above references fail to at least teach or suggest the design of the presently disclosed and claimed invention.